It's hard to predict what things will be like 10 years out, so "always" is a pretty strong word. :-)
However, I can safely make the following forecast:
a) Ubuntu won't be switching away from X.org in the short term. Certainly not for natty, and likely not natty+1 either. The exact schedule is doing to depend a lot on how quickly a lot of development work on compiz, unity, gtk and other bits can get done.
b) Even when we do switch, we'll be keeping X.org available for legacy applications. I don't know how long we'll keep it, but likely for several years at least.
c) Some drivers (like -fglrx and -nvidia) won't work with Wayland. There's also unusual graphics hardware, virtualization environments, and so on that won't meet Wayland's requirements for some time. So it's likely some "retro mode" that runs X just like today will be available, for users who prefer not to use Wayland.
d) Upstream X.org developers are supportive of moving the ecosystem to something Wayland-based. I would predict that eventually upstream will simply stop developing/supporting X.org, and that will be what brings X.org to an end. When will that happen? 10 years out? Maybe, I don't know.
In any case, don't panic. X.org isn't going away any time soon. Wayland is still in diapers.